The rat model of transitional cell (TC) carcinomas of the urinary bladder has many similarities to the disease in the human. These tumors can be produced by a variety of stimuli (foreign bodies and carcinogens) and have been shown to have common cross-reacting antigens on in vitro measurements of cell mediated cytotoxicity as well as antigens unique to each tumor which can be demonstrated by transplantation immunity experiments. We would like to investigate the relationship of the common and unique tumor antigens with antigens present in normal transitional epithelium of the bladder, and determine whether the nature of the carcinogenic stimulus makes a difference in the antigens expressed and whether these are neo-antigens. We would like to extend our E.M. studies of mouse bladder to study the E.M. characteristics (asymmetric unit membrane, desmosomes and A type virus particles) of these tumors in the rat in vivo and in tissue culture. If an A type virus similar to that found in the mouse is found to be present in the rat, then evidence for viral antigens would be sought. The mechanisms of cell mediated cytotoxicity have been investigated at a biochemical and functional level but very little at the microscopic anatomy level. We would like to follow up on some preliminary observation and use time lapse photography to understand the sequence of events that occur in lymphocyte mediated cytotoxicity between the lymphocytes and the target cell.